Personal respiratory protection devices are regularly used to supply clean air to a user of the device. The clean air is commonly available to the user by first drawing ambient air through a filter that is disposed in a filter cartridge. The filter cartridge typically is attached to a mask body that is worn on a person's face, over their nose and mouth. The ambient air is drawn through the filter from negative pressure created by the wearer's lungs. In other methods, clean air may be supplied to the user under pressure from a blower that forces the ambient air through a filter that is worn around the user's waist. This pressurized device is known as a powered air purifying respirator or PAPR. Alternatively, clean air has been furnished to the user from a pressurized tank, also known as a self-contained breathing apparatus or SCBA. In each of these techniques, a clean air supply source (such as a filter cartridge or a hose from a PAPR or SCBA) is connected to a mask body that is worn over the nose and mouth of the user. The eyes may be covered as well if the user desires full face protection.
A variety of systems have been developed in the respirator art to attach the clean air source to the respiratory mask. A common system uses a threaded filter cartridge that is attached to a corresponding threaded fitting on the respirator body—see, for example, U.S. Pat. Nos. 5,222,488, 5,063,926, 5,036,844, 5,022,901, 4,548,626, and 4,422,861. The threaded filter cartridges typically possess helical or advancing spiral threads that mate with a tapped collar or socket. Rotating the filter cartridge in an appropriate direction multiple times allows the cartridge to be attached to or removed from the mask body. A resilient, deformable gasket often is used to ensure that an airtight fit is maintained at the interface with the respirator body.
In lieu of threads, bayonet type closures have been used to attach clean air sources to respirators. The bayonet type closure has locking tabs and notches to secure the components together. The locking tabs may project from a filter cartridge and may engage the notches in an aperture on the respirator body. By rotating the filter cartridge in the appropriate direction, the cartridge engages the mask body—see U.S. Pat. Nos. 6,216,693 and 5,924,420. An audible device has been used in a bayonet system to indicate that the filter cartridge is properly coupled to the respirator face piece—see U.S. Pat. Nos. 4,934,361, and 4,850,346. A lug on the face piece has been provided with a détente ramp or cam that has an inclined surface. The surface is positioned to gradually deflect or deform a rib on the cartridge. As the cartridge and face piece are rotated relative to each other into a locking position, the cam engages the rib and causes the rib and lug to deflect until the rib abruptly drops off the end of the cam. The abrupt action produces the audible click. The benefit of using a bayonet-type fitting is that the cartridge can engage the mask body with a quick turn, usually less than about one-half turn—see, for example, U.S. Pat. No. 6,216,693 to Rekow et al.
Respirators that have snap-fit filter cartridges also have been designed as shown in U.S. Pat. No. 5,579,761 to Yushack et al. In this approach, the filter cartridge is instantaneously snapped into engagement with the mask body simply by pressing the cartridge against a corresponding receiving structure on the mask body. No rotational movement of the filter cartridge is needed.
Although the above-discussed respirators use various techniques for securing a clean air source such as a filter cartridge to a respirator, these techniques do have a number of drawbacks. For instance, the filter cartridges that are threaded to the respirator typically use a low thread pitch, which requires multiple rotations to complete the engagement. Bayonet structures tend to eliminate this difficulty, but these fittings require that the two components be appropriately aligned so that each locking tab is placed in each appropriate notch before the parts are rotated into engagement. And while snap-fit cartridges can be very convenient, the filter cartridge can nonetheless rotate relative to the mask body, even after being fully engaged.